1. Field of the Invention
The present invention relates to an automatic paper feed apparatus, particularly relates to an automatic paper feed apparatus which securely prevents skewing of transporting documents.
2. Description of the Related Art
As a first conventional example which prevents skewing of transporting documents, Japanese Utility Model Application Laid-Open No. 62-13948 proposes a technique using a document guide and a width determination plate.
Furthermore, as a second conventional example, Japanese Patent Application Lald-Open No. 9-240874 discloses a technique, which includes an image sensor for reading an image of a document, a feed roller provided In a position which faces the image sensor, a delivery roller provided on an upstream side of the image sensor, and a rubber plate member provided in a position which faces the delivery roller. A large friction area with a large coefficient of friction is formed on one portion of the feed roller in its longitudinal direction, and the rubber plate member is provided in a position of the delivery roller in its longitudinal direction which matches for the large friction area.
Therefore, according to the second conventional example, since the position of the large friction area of the feed roller matches for the position of the rubber plate member, a document can be transported suitably against a back tension generated on the document. Moreover, since the document is transported by a specified friction force even in right and left areas of the feed roller, all the documents can be transported uniformly. As a result, this technique produces an effect for efficiently preventing generation of pucker and skewing of the documents. Since the large friction area of the feed roller is provided in an approximately central portion of the longitudinal direction, the skewing of the documents at the time of transporting the documents by means of the feed roller can be efficiently prevented.
However, in the first conventional technique, since only the document guide and the width determination plate are used as means for preventing skewing, various mistakes such as miss-setting are frequently made, and thus the reliability is poor.
In addition, an object of the second conventional technique is to transport documents accurately against the back tension generated in the documents, and as a result skewing of the documents can be prevented just as a spillover effect. Therefore, similarly to the first conventional technique, skewing due to some reason cannot be reliably avoided.
The present invention is devised In such points in view in order to solve the above problems of the conventional techniques.
It is an object of the present invention to provide an automatic paper feed apparatus which is capable of preventing skewing of transporting documents completely and securely.
According to the present invention, a document tray is provided with a document positioning surface extending along a transporting direction in which a document is transported from the document tray. A main roller receives a document from the document tray by rotating in the transporting direction. A return roller is pressed against the first roller and rotates in a direction opposite to the transporting direction with a constant torque. Further, a skew-corrective roller which rotates in the transporting direction is provided to prevent skewing of the document In cooperation with the second roller and the document positioning surface.
A rotation speed of the skew-corrective roller rotates is preferably higher than that of the first roller. Further preferably, the skew-corrective roller is provided coaxlally with the second roller and at a position closer to the document positioning surface than the second roller.
A pressing means for pressing the skew-corrective roller towards the document is preferably provided to enhance the skew-correction capability of the skew-corrective roller.